What is the basilar membrane?

• A. A membrane that vibrates differently depending on sound frequency
• B. A structure that detects hair cell loss
• C. A portion of the cochlear outer wall
• D. The part of the inner ear responsible for balance

Answer: (A)

The basilar membrane is a long, flexible membrane inside the cochlea that vibrates in a way that depends on sound frequency. Its stiffness changes along its length, so high frequencies cause peak motion near the base while low frequencies peak toward the apex. This frequency-specific vibration creates a spatial code for pitch, with hair cells along the membrane translating those motions into neural signals. It isn’t about detecting hair cell loss, it isn’t a component of the outer cochlear wall, and it isn’t the structure responsible for balance (that role lies with the vestibular system).